The following lecture video shows and describes the mechanical advantage of a pulley: https://www.youtube.com/watch?v=bUkD1Hs_ahE
Pulley systems (“block and tackle”) were and still are widely used on sailing vessels to pull the sails. Type into your browser: block and tackle sailing ships images
(A pulley is defined as the wheel over which a belt or rope is run. Two or more pulleys together is called a “block”. “Tackle” refers to the rope.)
Blocks and tackle are similarly widely used on cranes. Type into your browser: block and tackle cranes images.